To everyone...
 
        Sorry for recent absence.  I was on leave for the last three days, and
will also be gone all of next week.  Unfortunately, my workaholic nature has
left me in a position that if I don't use twenty days of leave by 1 October, I
give them back to the government without reimbursement.
 
        But I will try to get caught up on my email today and tomorrow.  I have
made one phone call to Jessica Forys concerning Nikki, her ferret with adrenal
disease.  (It is always easier to cover some of these messages with a phone
call, so I always appreciate it when list members who need advice in a hurry
leave a phone number where I can reach them.
 
        Also concerning yeast tablets - I am not aware of a toxic principle in
yeast tablets, but yeast will cause diarrhea if given in high doses, simply by
upsetting the normal bacteria flora of the intestinal tract.  How much is too
much - sorry, I don't know.
 
        Finally, so that my leave wasn't a total waste - I have had several
requests for material on enlarged spleens.  So here goes...this material may be
reprinted (but not altered in any form) by anyone desiring to disseminate it and
is not protected by copywrite.
 
 
        The Mystery of Splenomegaly in Ferrets
 
        Splenomegaly, or the enlargement of the spleen, is one of the biggest
questions marks in ferret medicine today.  As a veterinary pathologist, over 15%
of my surgical biopsies from ferrets involve enlarged spleens.  As a ferret
owner, I have seen the spleens of several of my ferrets wax and wane in size
over the years.  In truth, one of my ferrets, who is now seven, has had an
enlarged spleen for most of his life.
 
        Fact -- we don't know what causes splenomegaly in the ferret.  There are
several theories, and I have come to my own conclusions (which I'll discuss in a
moment), but nobody really knows for sure.  Remember, as compared to dogs and
cats, we actually know very little about ferret disease.  While our knowledge
about this species grows daily, it will be many years before we amass the amount
of knowledge about ferrets that we have about more traditional companion
animals.
 
        First of all, what does the spleen do?  The spleen actually has several
functions. Its most important function is to act as a filter for the blood, ever
sifting the blood for bacterial agents or evidence of inflammation against which
its high population of white blood cells may mount an attack.   Additionally,
the spleen may act as a storehouse for blood - in some species, the spleen holds
as much as 15-20% of the total blood volume in reserve, so that it is
immediately available in times of stress.  Additionally, the spleen filters out
old red blood cells, which are trapped and subsequently digested by the white
blood cells that live there - the iron in these cells is reclaimed, and may be
used again if necessary, or it may be stored in the spleen against future needs.
 Finally, the spleen, in many species, and especially in the ferret, is where
new blood cells, of both the red and white varieties,  may be made, in addition
to the bone marrow.  Generally, this process occurs only where there is a
greater than normal need for these cells, (i.e., after hemorrhage, or during
systemic infections.)
 
        All this is fact.  Here's another fact:  only five percent of the
enlarged spleens that I see  in my pathology work are the result of some type of
neoplasm - lymphosarcoma being the most common neoplastic cause of splenomegaly.
 By far, the most common cause of splenic enlargement in ferrets is an
accumulation of massive numbers of developing red and white blood cells (known
as "extramedullary hemtopoiesis") .
 
         What causes splenic hematopoiesis?  Well, that's where the theories
begin.
 
        A).  The virus theory.  While several facilities have purported that a
virus causes this change, one has never been isolated, and in my opinion, this
theory is yet unproven.
 
        B).  The hypersplenism theory.   Several years ago, a case report was
published on a ferret with a large spleen, who had a progressively decreasing
blood count and a large spleen.  When the spleen was removed, the blood count
stabilized.  The theory arose that a malfunctionof the spleen was responsible
for excessive destruction of red blood cells.  The term "hypersplenism" was
applied to this phenomenon, after a condition in humans that bears some
resemblance.  However, this was an isolated case,  and has not been reported
again.
 
        C.  My theory, (well, it IS my article....)   This is not the result of
a formal study- this is simply my opinion, based on looking at hundreds of cases
of splenomegaly with associated clinical data. We know that the extramedullary
hematopoiesis arises as a result an increased demand for either red or white
blood cells, and there is no reason not to believe that this is the case in
ferrets.  But relatively few of these animals have evidence of anemia or recent
hemorrhage -- this leaves us with the more likely possibility of chronic
smoldering infections resulting in an increased demand for blood cells.  Well, I
certainly see my share of gastroenteritis, and renal infections, but that still
leaves a very large portion of animals with enlarged splens from a yet
undetermined cause.    However, when you go back and look at the ferrets which
had enlarged spleens at autopsy,  a large percentage of them  have evidence of
chronic gastritis due to infection by Helicobacter mustelae.  Helicobacter is  a
very common asymptomatic bacterial infection in ferrets which, over time, causes
a marked inflammatory response in the stomach and associated lymph nodes.  In
fact, it is the rare animal over 4 years of age that does not have microscopic
evidence of Helicobacter infection.  I believe that chronic infection in ferrets
due to gastric Helicobacter infection is responsible for a large number (not
all) cases of splenomegaly in the ferret.
 
        Now  let's look at another, probably more important issue  -  what we
should do about enlarged spleens.  Ferrets certainly do not need their spleens
to live - they tolerate splenectomy very well, and it is commonly  done.  But
rather than take out every big spleen we see, we need to set some criteria as to
when to remove them and when to leave them in.  Ideally, we would like to leave
them all in, but for various reasons, we are not always able to.
 
        Certainly, all spleens with lymphosarcoma or any other type of neoplasm
should come out immediately.  Veterinarians can tell when a spleen has a
neoplasm in it without taking it out - they can aspirate cells from it with a
needle and light anesthesia, or take a small piece of it during exploratory
abdominal surgery.  Qualified veterinary pathologists with experience with
ferrets can then look at the cells in the biopsy to determine whether they are
compatible with lymphosarcoma, other neoplasms, or are more consistent with a
proliferation of immature blood elements.
 
 
        In situations where a neoplasm is not present, the pros and cons of
splenectomy should be discussed with your veterinarian.  If an animal simply has
a large spleen, but shows no signs of illness or discomfort, it is safer for the
animal to leave it in.  However, if the animal shows signs of discomfort, such
as lethargy and a poor appetite, or a decrease in activity, then the spleen may
come out.  Finally, if the spleen is especially large, and the animal is very
active, there is a risk of splenic rupture, and once again, splenectomy should
be considered.
 
        As of yet, the jury's still out on big spleens in ferrets.  However, we
do know that all of these cases should be investigated by your veterinarian, and
appropriate steps taken to insure your pet's health and well-being.
 
 
       Bruce Williams, DVM                 Department of Veterinary Pathology
       [log in to unmask]         Armed Forces Institute of Pathology
       (202) 576-2453/2454                 Washington, D.C.  20306-6000
 
[Posted in FML issue 0909]